Preach THAT brother!For a military man, he doesn't decide what is a just war or what isn't. You are correct, first it is up to congress and then the president to decide whether to use force or not. The populace can make its voice heard. The soldier must follow the orders and directives that come down the chain of command.
What does supporting the troops mean? That definition probably is left up to the individual. It doesn't mean treating soldiers like some of the U.S. population did after they returned from Vietnam. I can remember the hostile greetings some of these war veterans received at the hands of the anti-war crowd. During that time it seemed the soldier was to be blamed and not the elected leaders that sent them into harms way.
I think the bottom line is just treating military members with respect. You do not have to do anything for them, just don't shout "baby killer," or spit upon them and threat them like they were pariah. Most of the soldiers serving in Vietnam didn't want to be there in the first place. If one is against any particular war, complain, demonstrate, write letters to your congressman, senators and the president and to newspapers, but don't take it out on the soldier.